Cabinet ministers are allowed to campaign freely on either side of the debate, but the official government position is in favour of staying in a reformed EU.

The official government analysis of UK membership of the EU is required by law under the EU Referendum Act, which paved the way for the in-out referendum on EU membership.

The paper looks at possible alternative arrangements for relations with the EU if the UK voted to leave, including those adopted by Norway, Switzerland and Canada, as well as the option of reverting to World Trade Organization (WTO) rules.

The government paper is expected to say each alternative arrangement outside of the EU would carry serious risks, threatening the UK economy and hitting business with higher costs through new tariffs on UK exports.

Meanwhile, former Conservative Chancellor Lord Lamont has come out in favour of an EU exit, saying the vote is a once-in-a-generation opportunity .

Writing in the Telegraph, the peer insisted the UK could succeed economically outside of the EU, and argued that a vote to leave would give Britain control of immigration.

It is a central question in this referendum debate: what would be the practical, long-term consequences if Britain voted to leave the EU?

An assessment from the government, whose position is to remain in the union, will highlight what pro-EU ministers consider to be flaws in the alternatives.

The Remain campaign wants to put pressure on its opponents to explain what they think life after membership would look like.

Those campaigning to leave say these arguments ignore the fact the UK would negotiate its own free trade arrangement, not copy one settled by smaller economies. The EU they argue would need an agreement as much as Britain.

The government document will say Norway and Switzerland s trading arrangements outside the EU require them to make financial contributions, accept the EU principle of free movement of people and be subject to other EU laws.

Meanwhile, Switzerland and Canada s arrangements provide only limited access to the single market, it will add.

Mr Hammond said analysis showed that every alternative to remaining in a reformed EU would leave Britain weaker, less safe and worse off .

Speaking on BBC Breakfast, he added: This is going to be a divorce, if we decide to leave, and as with any divorce it is likely to get messy. It will take a long time to sort out the disentanglement of our affairs.

He said British businesses, consumers and jobs would then be left in limbo , and called on pro-exit campaigners to set-out a model for how the UK would negotiate with the EU in the event of it leaving the union.

But Mr Duncan Smith one of five cabinet ministers campaigning in favour of a vote to leave the EU said the government was in denial about the risk of remaining a member.

This dodgy dossier won t fool anyone, he said, adding that the real uncertainty is the future of the EU project.

The truth is, we won t copy any other country s deal.

We will have a settlement on our own terms and one that will return control of our borders, and money to Britain.